Numerous safety belt systems have been employed and proposed which include a spool retractor or other webbing storing device, commonly for lap or shoulder belt or both. Examples are two retractors or single dual spool retractor in a three point system; a two point system employing single retractor for lap or shoulder belt; and a single loop system for belt and shoulder employing a single retractor. In such systems a number of locations for the retractors have been used, such as door, floor, pillar, roof, seat, console and in some cases, as an alternative for a spool retractor, other webbing storing devices may be employed such as linear storage units. The systems may be "passive" to assure occupant use or "active" providing occupants with a use option. In some systems inertia devices are employed to lock the retractor spools in response to vehicle deceleration requiring belt restraint.
Common to all such systems known to applicants before the present invention, whether involving inertia actuated or other lock up of the retractor, no provision has been made to prevent occupant excursion under belt load arising from belt extension in the entire system. Such yield, partially due to stretch in the webbing per se between the locked retractor and opposite belt end and partially to the multiple wraps of webbing on the spool tightening under belt load, is particularly detrimental in the case of shoulder belts found to yield in some cases sufficiently for the driver's body or head to impact the steering wheel and even for front seat occupants heads to hit the windshield.
The problem is further aggravated in the case of door mounted retractors particularly of the passive type, where sufficient webbing must be employed to accommodate full door opening during occupant entry and exit while the inside end remains anchored, which in a typical case may involve a cut length of webbing in the order of 96" for a shoulder belt and 78" for a complementary lap belt. This "excursion" problem has been known since the inception of belt retractors and some attempt has been made to mitigate it, e.g. by load responsive junction rings which proportion tension between belt and shoulder segments of a single loop system to thereby prevent "submarining" under the lap belt; also by a static loop for a shoulder belt which applies frictional resistance to passage of webbing under load. However, no prior solution is known which completely locks the webbing with zero slip from a static loop in close proximity to the occupant thereby limiting excursion due to belt stretch which is substantially confined to the relatively short length of webbing immediately employed in restraining the occupant.
The closest known prior art relevant to the present invention, as disclosed herein in a door mounted dual reel inertia retractor for lap belt and shoulder belts with comfort feature, include the following references:
Comfort feature mechanisms are disclosed in U.S. Pat. Nos. 4,149,683 and 4,165,054 which relieve belt retraction tension on the occupant upon slight protraction.
A single passive lap belt is disclosed in U.S. Pat. No. 3,771,814 employing a door mounted retractor.
A single passive shoulder belt installation is disclosed in U.S. Pat. No. 4,181,326 employing a door mounted retractor having a static loop guide on the door frame above the occupant's shoulder height. The webbing of the shoulder harness again involves a length sufficient to result in the problem of excessive belt extension.
A floor mounted dual reel retractor is disclosed in prior U.S. Pat. No. 4,135,683 which requires manual buckle release not suitable for a passive system.
Static loop webbing guides are known which normally permit free passage and frictionally impede web passage in response to predetermined back tension. However, a minimum back tension ratio in the order of 1:2 rather than 100% snubbing limits the effectiveness for reducing belt extension under load.
Snubbers employed in adjusting belt length in linear belt systems are known such as commonly used in adjusting length in aircraft and passenger car seat belts wherein the adjustment device is manually moved to an unlocking angle to permit lengthening and the surplus belt end is pulled freely through the device after buckling to take up the slack.